1. Field of the Invention
The present invention is within the field of orthodontics and relates to an improvement in an orthodontic appliance used for expansion of a patient's dental arch or upper jaw bone and alveolar shifting of teeth.
2. Description of Related Art
Known orthodontic devices as shown in FIG. 7, are constructed so that bases 1 and 2, supported by two right-left guide rods 3, are capable of opening and closing. A threaded rod 4 having reversed threads is screwed into the central parts of the bases 1 and 2 so that the pair of bases 1 and 2 can be made to approach or separate on guide rods 3 by rotating operating part 4a of the threaded rod 4 with tool 5.
When using this orthodontic appliance in clinical practice for expansion of the upper jaw bone, as shown in FIG. 8, the pair of bases 1 and 2 are soldered to each connecting arm 6a of fixed type expansion apparatus 6, and after attaching the sides of bases 6b of expansion apparatus 6 to tooth surfaces T by means of adhesive or bands (not illustrated), threaded rod 4 is rotated in a prescribed direction by means of tool 5. When each base 1 and 2 shifts away from one another, the dental arch of the patient expands from the orthodontic force obtained by the shifting, and it becomes possible to expand the upper jaw bone by diastematic stitching of the palate.
When used in clinical alveolar shifting of tooth T1, as shown in FIG. 9, the embedded pair of bases 1 and 2 are connected between fixed side bed 7a and shifting side bed 7b of removable bed apparatus 7. Fixed side bed 7a is attached to the side of normal teeth T2 by means of clasp 8, and after attaching shifting side bed 7b to tooth T1 that requires treatment by means of clasp 8, threaded rod 4 of the orthodontic appliance is rotated in a prescribed direction in the same manner as before. Thus, when each base 1 and 2 shifts in the opening direction, it becomes possible to shift tooth T1 in the prescribed direction by the orthodontic force obtained from such shifting.
Such prior orthodontic appliances attempt to obtain their orthodontic force by the shifting of base 1 that accompanies the rotation of threaded rod 4 during expansion of the upper jaw bone and during shifting of teeth. Because of this, when the expansion of the upper jaw bone and the shifting of teeth advance in the course of treatment, it becomes necessary to separate the pair of bases 1 and 2 gradually by repeated rotations of threaded rod 4 in order to obtain the orthodontic force required at each time. Because the adjustments in orthodontic force must be ultimately done by the shifting of bases 1 and 2 that accompanies the rotation of threaded rod 4, there is difficulty in applying the ideal orthodontic force because each adjustment is imparted as a displacement rather than as a force.
Furthermore, these adjustments of the orthodontic appliance are not always made by specialists in orthodontics, and in some instances must be made by the patient or by a person caring for the patient. In these cases, the above described adjustment problem becomes more pronounced.
Consequently, it is difficult to properly adjust the force when mechanically shifting the pair of bases 1 and 2 of known orthodontic appliances to displace them by means of rotation of threaded rod 4.
Accordingly, it is an object of the present invention to provide an orthodontic appliance which reduces or eliminates the need for periodic adjustments in orthodontic force during treatment.
It is a further object of the invention to provide an orthodontic appliance which is capable of exerting a substantially constant orthodontic force continuously to teeth.